Alternating current motors are used in many industrial applications where it is desired to operate devices, such as compressors, at high speed. Typically, where high powers are required, the motor is designed to be powered by a three phase alternating current source. The three phase alternating current source generates three electrical currents of the same frequency which are out of phase from one another by one third of a cycle. Thus, when one of the electrical currents reaches its maximum amplitude, one of other electrical currents will reach a maximum amplitude one third of a cycle later and the third of the electrical currents will reach its maximum amplitude two thirds of a cycle later. In a three-phase electric motor separate windings are provided in a stator and are connected to each other and the three phase alternating current source so as to generate a magnetic field that rotates around the stator. This rotating magnetic field is able to induce motion in a rotor, rotating within the stator by provision of pole pieces on the rotor. The rotating magnetic field acts upon pole pieces formed by bars, coils or permanent magnets to induce a rotation of the rotor.
Three phase electric motors can incorporate magnetic gearing to either increase the speed of a rotor or decrease the speed of a rotor and impart more torque by such a rotor. An example of this is shown in U.S. Patent Appln. No. 2011/0163623. In this publication, an inner rotor is provided that contains windings which form electromagnets when the windings are supplied by an electric current. An outer rotor rotates around the inner rotor that has a number of pole-pieces. Surrounding the outer rotor are a series of permanent magnets connected to a fixed stator. The pole pieces of the outer rotor allow fields of the permanent magnets in the fixed stator to interact with the windings of the inter rotor so that rotation of the outer rotor causes the inner rotor to rotate and vice versa. The inner rotor rotates at a higher speed than the outer rotor. An outer stator is provided to rotate the inner rotor. When a three phase alternating current is applied to windings contained in the outer stator and power is supplied to the windings of the inner rotor, the inner rotor will rotate in a manner described above and at the same speed as the rotating magnetic field produced by the three phase alternating current and in the same direction. Such rotation will induce rotation in the outer rotor at a lower speed and a higher torque. The outer rotor can thereby be connected to a load that requires low speed and high torque. Thus the outer rotor containing the pole pieces is magnetically geared to the inner rotor by means of the permanent magnets connected to the fixed stator. It is to be noted that in a magnetic gear arrangement shown in GB 2493484 A, the permanent magnets can be replaced by electromagnets and the windings of the inner rotor can be replaced by permanent magnets. In such a geared arrangement, rotation of the outer rotor containing pole pieces will induce rotation in the inner rotor containing the permanent magnets at a higher speed than the outer rotor.
A motor containing a geared arrangement such as shown in the published patent applications referenced above, contemplates that the inner high speed rotor to rotate at a speed induced by the three phase alternating current applied to outer winding driving the inner high speed rotor. As will be discussed, among other advantages, the present invention provides an electric motor in which the inner high speed rotor will rotate at a greater speed than the rotating magnetic field produced in the stator.